iPhone batteries, like all rechargeable batteries, are consumable components that become less effective as they age. Each original battery after 300 to 500 cycles diminishes its full capacity down to 80% or even less. Check your battery health in Settings/Battery/Battery Health (Beta) the feature is available if your software is up to date. We fix phones and use these batteries ourselves. All our refurbished phones show full capacity and have good battery live.All batteries are tested with a multimeter before dispatch and are 100% safe and working. Same day or next day dispatch.